Coating die with expansible chamber device

ABSTRACT

An apparatus comprising a die having at least one application slot. The slot is in fluid communication with a die cavity. An expansible chamber device is disposed within the die cavity and changes volume in response to changes in pressure within the expansible chamber device. Another aspect of the invention is a method of translating a liquid through a die. A coating die is provided. The die comprises at least one applicator slot in fluid communication with a die cavity. An expansible chamber device is disposed within the cavity. The expansible chamber device is actuated by changes in the fluid pressure within the expansible chamber device. The liquid is translated through the die and delivered from the application slot at intervals corresponding to actuation of the expansible chamber device. Another aspect of the invention is a method for forming a die. An apparatus comprising a die having at least one applicator slot in fluid communication with the die cavity is provided. An expansible chamber device is disposed within the die cavity.

BACKGROUND

The invention relates generally to coating and extruding apparatus. Moreparticularly, the present invention relates to coating and extrudingapparatus that can be used to vary the transition rate of a fluid out ofa die.

Using extrusion dies to form films and coating dies to coat a fluid ontoa substrate is known. It is also known to coat a fluid onto a web in aseries of discrete patches, or to extrude a film intermittently (e.g.onto a chilled roll). For example, one known way to coat intermittentlyonto a substrate is to use a flexographic coating process. Flexographiccoating processes use rolls having raised surfaces that are pressedagainst a substrate. Each raised surface on the roll transfers a “patch”of coating fluid to the substrate. Using the flexographic coatingprocess has many limitations. For example, in order to apply more thanone type of fluid (e.g., different colors) to specific areas on a movingweb requires a series of coating stations (typically requiring largerolls) with drying ovens positioned after each coating station. Thefluids are typically applied by a coat/dry, coat/dry, . . . , coat/dryprocess. Thus, in order to coat multiple fluids multiple pieces of largeexpensive equipment must be used. Additionally, the repeat pattern onthe roll determines the location of each patch of fluid and the spacingof the patches cannot be varied without changing the pattern of theraised surfaces or removing or replacing the rolls themselves. Thus, theoverall repeat length of a patch series is limited and set by thecircumference of the flexographic cylinders. Patch sizes cannot bechanged except by changing the cylinders.

It is also known to provide a coating apparatus that has a main pumpthat provides the major supply of fluid to a coating die. Dosing pumpshave been used to add and retract fluid in the die for starts and stops,respectively, of the coating process. In other words, the main pumpprovides a continuous supply of fluid to maintain a coating process andthe dosing pump acts concurrently, adding or subtracting fluid to thedie.

It is known to provide an apparatus for coating a pattern of spaceddiscrete patches on the web of material by using a metering pump thatsupplies coating fluid to the internal cavity of an extrusion (orcoating) die from a fluid reservoir. The dies may also include a pistonalone or in combination with a pump that can be translated into or outof the cavity to control the flow of fluid out of the extrusion/coatingdie. Typically, by translating the piston into the cavity of the die,material is translated out of the die (e.g., onto a substrate).Translating the piston out of the cavity typically stops translation ofthe fluid out of the die. One example of this concept are ram dieswherein the driving force for expelling the material from the die isprovided directly by a long, thin piston positioned along the internalcavity of the die and along its width. These types of coating apparatusmay also utilize a diaphragm, clamped so as to change the volume withina draw-in chamber when directly attached to a piston. The apparatusdescribed above present the difficulty of providing for smooth motion ofthe piston or ram without contamination of the material being coated orextruded.

BRIEF SUMMARY OF THE INVENTION

The invention includes an apparatus comprising a die having at least oneapplication slot. The slot is in fluid communication with a die cavity.An expansible chamber device is disposed within the die cavity andchanges volume in response to changes in pressure within the expansiblechamber device.

Another aspect of the invention is a method of translating liquidthrough a die. A coating die is provided. The die comprises at least oneapplicator slot in fluid communication with a die cavity. An expansiblechamber device is disposed within the cavity. The expansible chamberdevice is actuated by changing the fluid pressure within the expansiblechamber device. Liquid is delivered from the application slot at avariable rate influenced by the actuation of the expansible chamberdevice.

Another aspect of the invention is a method for forming a die. Anapparatus comprising a die having at least one applicator slot in fluidcommunication with the die cavity is provided. An expansible chamberdevice is disposed within the die cavity.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will be further explained with reference to thedrawing figures referenced below, wherein like structure is referred toby like numerals throughout the several views.

FIG. 1 is a perspective view of a portion of a coating line including acoating die according to the present invention.

FIG. 2 is a bottom view of the inventive coating die and some of itssupporting equipment, shown with some of the die partially removed sothat the expansible chamber device can be visualized.

FIG. 3 is a cross-section end view of the die of FIG. 2.

FIG. 4 is a schematic view of one embodiment of a control mechanismsuitable for use with the present invention.

FIG. 5 is a schematic view of a second embodiment of a control mechanismsuitable for use with the present invention.

FIG. 6 is a schematic view of a third embodiment of a control mechanismsuitable for use with the present invention.

Patents, patent applications, and publications disclosed herein arehereby incorporated by reference (in their entirety) as if individuallyincorporated. It is to be understood that the above description isintended to be illustrative, and not restrictive. Various modificationsand alterations of this invention will become apparent to those skilledin the art from the foregoing description without departing from thescope of this invention, and it should be understood that this inventionis not to be unduly limited to the illustrative embodiment set forthherein.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION

Referring now to FIG. 1, a perspective view of a portion of a coatingline 10 including a coating die 12 according to the present invention isillustrated. The die 12 is depicted applying discrete patches 14 of afluid material 15 to a web 16 moving in direction “A” away from roller18. It should be noted that while a coating process is illustrated inFIG. 1, this is shown for exemplary purposes only. The invention can beused in other coating or extruding applications without depicting fromthe spirit and scope of the invention. For example, inventive die 12could be used to extrude fluid onto a chilled roll, among otherapplications. The die 12 conveniently includes a first portion 20 and asecond portion 22. Although a two-portion die 12 has been described andillustrated, the ordinary artisan will know that it is sometimes moreconvenient to provide the die as a single piece or as a multiple piececonstruction. In the depicted embodiment, an extruder 24 supplies thematerial to be applied to web 16 into the die 12 through a materialsupply port 26. Other methods for providing continuous or intermittentflow into a die are known to a person of ordinary skill in the art, andare considered to be within the scope of the invention. For example,some preferred embodiments, a positive displacement pump 27 is used tometer flow into the material supply port 26, so as to control moreaccurately the starting and stopping of material flow, and to preventreverse flow back towards the extruder 24.

As will be discussed with more particularity in connection with FIGS. 2and 3 below, the present invention can coordinate delivery the of fluidmaterial 15 to the die 12 and the control of the volume of theexpansible chamber device 42 (illustrated in FIG. 2) within the die 12.The control of the volume within the expansible chamber device 42 isgenerally accomplished by varying the fluid pressure within theexpansible chamber device 42. For example, the volume of a fluid withinthe expansible chamber device 42 may be measured and varied (thusvarying the fluid pressure) to control the volume of the expansiblechamber device 42, or the pressure of the fluid within the expansiblechamber device 42 may be directly measured and varied to control thevolume of the expansible chamber device 42. With such coordination, veryfine control of the timing of the translation of fluid material 15 fromthe die 12 can be achieved. The embodiment illustrated in FIG. 1provides this coordination utilizing a process controller 28, (e.g., aprogrammable logic controller) in communication with the extruder 24 viacontrol line 30. The process controller 28 gives commands tointermittently start and stop the delivery of fluid material 15 to thedie 12, and thus provides one control over the placement of patches 14on the web 16. Additionally, the positive displacement pump 27 can becontrolled by the process controller 28 as well. While this illustrationdepicts discrete patches on a moving web, the invention may also be usedto create regions of varying coating thickness, rather than regionswhere the coating is not applied at all. Further, the application ofcoating liquid to discrete articles, rather than only a continuous,indefinite length web is also contemplated.

In the embodiment illustrated, the process controller 28 communicatesvia control line 32 with control device 34, giving commands for theregulation of pressure within the expansible chamber device 42(illustrated in FIG. 2) via fluid port 38. For example, fluid pressureinside the expansible chamber device 42 can be increased or decreased byincreasing or decreasing the volume of fluid inside expansible chamberdevice 42. Alternatively, fluid pressure inside the expansible chamberdevice 42 can be increased or decreased by inserting a mechanicalplunger inside the expansible chamber device 42, displacing existingfluid within the expansible chamber device 42.

A bleed valve train 40 may also be connected to die 12 to remove airfrom the hydraulic system. Again, it should be noted that the processdevices described (e.g., process controller control device 34, and bleedvalve train 40) are described and shown for exemplary purposes only.Other embodiments for controlling and configuring the die may be usedwithout departing from the spirit and scope of the invention.

FIG. 2 illustrates a bottom view of the die 12 and some of itssupporting equipment with the second portion 22 (shown in FIGS. 1 and 3)removed from the die 12. One embodiment of expansible chamber device isillustrated at 42. First portion 20 can now be seen to partially definea die cavity 44. In the illustrated embodiment, the die cavity 44 isalso defined by the second portion 22 that has been removed from thisfigure, however any die configuration which defines a cavity is withinthe scope of the invention. It will be noted that in the depictedembodiment, the expansible chamber device 42 extends across an entirewidth 45 of die cavity 44, and this is convenient for many of the mostuseful applications of the present invention. However, other end useapplications may configure the expansible chamber device 42 such that itextends only through one or more portions of the width of die cavity 44.Also considered within the scope of the invention are embodiments wherethe expansible chamber device 42 is defined in part by the surface ofthe die cavity 44, e.g an elastomeric bladder making an edge seal withthe typically metal walls of the first portion 20 or the second portion22.

The expansible chamber device 42 is in fluid communication with fluidpressure line 36 through fluid port 38. As discussed previously, varyingthe pressure of fluid medium 49 within expansible chamber device 42changes the volume of the device 42. In other words, the fluid medium 49engages (or is “coupled”) to the wall (or walls) 42A of the expansiblechamber device 42 such that a change in the amount of fluid pressure(e.g. due to a change in volume of the fluid medium 49 or due to adisplacement of the fluid medium 49) expressed against the walls of theexpansible chamber device 42 will cause the wall 42A to moveproportionately to this change in pressure. This assumes that pressurechanges on the other side of the wall 42A remain small relative to thechanges in pressure within the expansible chamber device 42. Utilizingfluid medium 49 to transfer force to wall 42A of the expansible chamberdevice 42 (versus, for example, a mechanical connection) providestranslation of force substantially equally across all areas of the wall42A engaged by fluid medium 49 since force is translated throughout thefluid and to any portion of wall 42A couple or engaged by the fluidmedium 49. This transfer of force occurs at a very high rate.

In one embodiment, the expansible chamber device 42 is comprised of apolymeric tube (as illustrated), but any suitable physical shape iscontemplated to be within the scope of the invention. One advantage ofthe invention, which particularly accrues to embodiments where theexpansible chamber device 42 is a polymeric tube, is that it isparticularly easy to retrofit onto existing production dies, since itcan be installed by drilling a hole into the die cavity 44 through thewall 44A of the die 12 and inserting the device 42. Additionally,utilizing cylindrical geometry (e.g., a tubular shape) for theexpansible chamber device 42 allows the change in volume per unit lengthof the expansible chamber device 42 in response to a change in the fluidpressure within itself to be substantially equal across the entire widthof the die cavity. This allows the die 12 to be designed such thatactuating the expansible device 42 translates fluid material 15uniformly out of die 12 along longitudinal dimension 45. It is alsocontemplated that thin wall metal tubes or bellows could be used,increasing the responsiveness of the tube in changing diameter therebyproviding a high level of dynamic performance to the die 12. Theconfiguration of the inventive apparatus also provides for minimalmoving parts inside the die. The inventive apparatus allows for thetranslation of fluid material 15 out of the die 12 with minimal (if any)lubrication required for the expansible chamber device 42.

Material supply port 26 has an outlet 46 in communication with diecavity 44 so that the fluid material 15 to be coated may enter the diecavity 44. The die cavity 44 communicates with slot region 48. Asillustrated in FIG. 3, slot region 48 of first die portion 20 combineswith second portion 22 to define an applicator slot 50. In oneembodiment, slot region 48 extends the entire width 45 of die cavity 44.In other embodiments, slot region 48 may extend only along a portion ofthe width 45 of die cavity 44.

It can also be appreciated that bleed valve train 40 is also in fluidcommunication with the expansible chamber device 42 via conduit 52. Thebleed valve train 40 is optional, and not needed in all coating systemsconstructed according to the present invention. However, in hydraulicsystems it is sometimes useful to include a mechanism to purge unwantedgas from the hydraulic lines in order to sharpen the system response.Suitable elements are further illustrated in FIG. 4.

As discussed above, control over the extruder 24 and positivedisplacement pump 27 typically provide primary control over thetranslation of the fluid material 15 out of die 12, through slot region48. However, due to many reasons such as the mass of the extruder'smechanism, and the mass and viscosity of the material to be translated(i.e., extruded or coated) using only pump 27 and/or extruder 24 doesnot to control the starting and stopping of material flow with thedegree of precision required. In the present invention, the expansiblechamber device 42 can be used to precisely control the starting,stopping and speed of the translation of fluid material 15 through slotregion 48 by precisely adjusting the volume of die cavity 44. In theillustrated embodiment it will be appreciated how a sudden pressure risewithin the expansible chamber device 42 will expand the diameter of theexpansible chamber device 42 (illustrated by dotted lines) which causesexpansible chamber device 42 to occupy more volumetric area within diecavity 44, displacing fluid material 15 within die cavity 44. Thus,expansible chamber device 42 can initiate the delivery of fluid material15 through slot region 48. In one application, this “actuation” of theexpansible chamber device 42 can begin the laying down of a patch ofmaterial on a substrate. Due to the placement of the expansible chamberdevice 45 of the cavity 44 there is a constant change in volume of thedie cavity 44 across the width 45 of the die cavity 44 and fluidmaterial is translated evenly out of the slot region 48 across theentire width of the die. At the trailing edge of the patch, a suddenpressure drop within the expansible chamber device 42, and theconsequent volume decrease of the expansible chamber device 42 (shown bydotted lines), causes the material to “snuff back”, and does it evenlyacross the entire width of the slot region 48. It will be furtherappreciated, that in some applications (e.g., particularly when the diesize is small and when the coating fluid has low viscosity) that theexpansible chamber device 42 could provide primary control over thetranslation of fluid material from the die 12 (i.e., without utilizingpump 27 and/or extruder 24).

Referring to FIG. 3 (a cross-section end view of the coating die 12 ofFIG. 2), first portion 20 is seen attached to second portion 22, and itcan be more readily appreciated how the two die portions define the diecavity 44 and the applicator slot 50 having a length extending generallyalong the width of the cavity 44. In one contemplated embodiment, thefluid medium 49 used to change the volume of the expansible chamberdevice 42 is air, while another embodiments the fluid medium 49 is aliquid such as water or oil. The use of an incompressible fluid as thefluid medium 49 (e.g. water or oil) provides additional inventiveadvantages, especially when using a volume displacement device to serveas the control mechanism 34. When incompressible fluid is used as thefluid medium 49, the volume of fluid medium 49 added or subtracted fromthe expansible chamber device 42 can be used to calculate thedisplacement of the expansible chamber device 42, and thus the volume offluid material 15 displaced in the die cavity 44. This is due to thefact that the change in volume of the expansible chamber device 42 isrelated linearly to the amount of fluid medium 49 added or subtracted tothe expansible chamber device 42.

The expansible chamber device 42 may be fabricated from silicone,urethane, or fluoroelastomers such as Fluorel™ or Viton™ or any othermaterial compatible with the fluid within the expansible chamber device,the fluid to be coated, and the temperature at which the coating occurs.

A schematic view of one embodiment of a control mechanism 34, whichvaries the volume of the fluid material 49 within the expansible chamberdevice 42, is illustrated in FIG. 4. A hybrid pneumatic/hydraulic systemis illustrated, with hydraulic fluid being the working fluid to controlthe volume of the expansible chamber device 42. With the working fluidbeing virtually incompressible, it is convenient to use a volumedisplacement device 60. The positive displacement device 60 includeshydraulic cylinder 62 and pneumatic cylinder 64 connected by a commonrod 66. Pneumatic cylinder 64 immediately includes a stroke limiter 68and a spring bias 70 urging rod 66 towards the stroke limiter. Anapparatus of this type is commercially available as model number P250V225 BTG available from Williams Instrument Company of Ivyland, Pa.Pneumatic cylinder 64 is conveniently controlled by a solenoid valve 72that reacts to control signals along control line 32.

In this embodiment hydraulic fluid is conveniently provided into thesystem from a reservoir 74. An overflow valve 76 and a check valve 78conduct fluid from the reservoir 74 towards hydraulic cylinder 62. Inthe depicted embodiment bleed valve train 40 includes overflow valve 80and bleed valve 82. In this embodiment the volume of fluid medium 49displaced in the volume displacement device 60 can be monitored tocontrol the change in volume of the expansible chamber device 42. Thechange in volume of fluid medium 49 within expansible chamber device 42changes the fluid pressure within expansible chamber device 42, alteringthe volume of the expansible chamber device 42. It should be understoodthat the control mechanism 34 described and illustrated with respect toFIG. 7 is one exemplary embodiment that may be used in the currentinvention. Other control mechanisms 34 may be utilized without departingfrom the spirit and scope of the invention.

A schematic view of a second embodiment of a control mechanism 134 isshown in FIG. 5. In this embodiment, a pneumatic system is illustratedusing solenoid valve 72 placed directly in series with expansiblechamber device 42. In this embodiment air pressure (or othercompressible fluid) is provided from fluid pressure line 36 source (suchas factory air pressure line) and directed through the solenoid valve 72which adjusts the air pressure directed to the expansible chamber device42 according to control signals along control line 32. Overpressurevalve 80 may also be provided. Thus, in this embodiment fluid pressurewithin expansible chamber device 42 is monitored to control change involume of the expansible chamber device 42.

A schematic view of a third embodiment of a control mechanism 234 isillustrated in FIG. 6 using substantially the same components as thoseillustrated in FIG. 4 with the exception that rod 66 extends directlyinto expansible chamber device 42. Extending rod 66 into expansiblechamber device 42 allows rod 66 to displace fluid medium 49 withinexpansible chamber device 42 without adding or subtracting fluid fromexpansible chamber device 42. Changing the displacement of fluid medium49 within expansible chamber device 42 changes the fluid pressure withinthe expansible chamber device 42, changing the volume of the expansiblechamber device 42.

The present invention addresses the disadvantages inherent in thedevices described above by provides a die for coating or extrusionhaving a die cavity and adjacent to an applicator slot, and anexpansible chamber device disposed within the cavity. The expansiblechamber device responds with a change in its volume to a change in thefluid pressure within itself, and preferably the expansible chamberdevice extends across substantially the entire width of the die cavity.In preferred embodiments, the change in volume per unit length of theexpansible chamber device responding to a change in the fluid pressurewithin itself is substantially equal across the entire width of the diecavity. Conveniently, in one of the embodiments of the present inventionthe apparatus is connected to a pressure control mechanism in fluidcommunication with the expansible chamber device and adapted to controlthe fluid pressure within the expansible chamber device.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. A method of translating liquid material through a coating diecomprising: providing a coating die having at least one applicator slotin fluid communication with a die cavity, wherein the die cavityexhibits a volume; disposing an expansible chamber device within the diecavity, wherein the expansible chamber device exhibits an initial volumeless than the volume of the die cavity; controlling the pressure of anincompressible fluid within the expansible chamber device to vary thevolume of the expansible chamber device by increasing the pressure ofthe incompressible fluid within the expansible chamber device, therebyincreasing the volume of the expansible chamber device from the initialvolume to an expanded volume less than the volume of the die cavity, andthereafter decreasing the pressure of the incompressible fluid withinthe expansible chamber device, thereby decreasing the volume of theexpansible chamber device from the expanded volume; and deliveringliquid material from the applicator slot at a variable rate influencedby the volume of the expansible chamber device.
 2. The method accordingto claim 1 further comprising the step of extending the expansiblechamber device across substantially the entire width of the die cavity.3. The method according to claim 1 wherein the expansible chamber deviceis defined in part by the surface of the die cavity.
 4. The methodaccording to claim 1 wherein the expansible chamber device is actuatedwith a pressure control mechanism in order to provide precise control ofthe timing of the delivery of the liquid material from the applicatorslot.
 5. The method according to claim 4 wherein the pressure controlmechanism is a volume displacement device.
 6. The method according toclaim 1 wherein the incompressible fluid is selected from water and oil.7. The method according to claim 1 wherein the incompressible fluidpressure is created with a liquid.
 8. The method according to claim 1wherein the expansible chamber device comprises a tube.
 9. The methodaccording to claim 1, wherein the expansible chamber device is comprisedof a polymer.
 10. The method according to claim 1, wherein theexpansible chamber device is comprised of a metal.